diff --git a/src/challenge-module/challenge-credential.hpp b/src/challenge-module/challenge-credential.hpp
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+++ b/src/challenge-module/challenge-credential.hpp
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+/**
+ * Copyright (c) 2017, Regents of the University of California.
+ *
+ * This file is part of ndncert, a certificate management system based on NDN.
+ *
+ * ndncert is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation, either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * ndncert is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License along with
+ * ndncert, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndncert authors and contributors.
+ */
+
+#ifndef NDNCERT_CHALLENGE_CREDENTIAL_HPP
+#define NDNCERT_CHALLENGE_CREDENTIAL_HPP
+
+#include "../challenge-module.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+/**
+ * @brief Provide Credential based challenge
+ *
+ * Credential here means the certificate issued by a trust anchor. Once the requester
+ * could proof his/her possession of an existing certificate from other certificate, th
+ * requester could finish the challenge.
+ *
+ * The main process of this challenge module is:
+ *   1. Requester provides a certificate signed by that trusted certificate as credential.
+ *   2. The challenge module will verify the signature of the credential.
+ *
+ * There are several challenge status in EMAIL challenge:
+ *   FAILURE_INVALID_SIG: When the credential cannot be validated.
+ */
+class ChallengeCredential : public ChallengeModule
+{
+public:
+  ChallengeCredential(const std::string& configPath = "challenge-credential.conf");
+
+PUBLIC_WITH_TESTS_ELSE_PROTECTED:
+  JsonSection
+  processSelectInterest(const Interest& interest, CertificateRequest& request) override;
+
+  JsonSection
+  processValidateInterest(const Interest& interest, CertificateRequest& request) override;
+
+  std::list<std::string>
+  getSelectRequirements() override;
+
+  std::list<std::string>
+  getValidateRequirements(const std::string& status) override;
+
+  JsonSection
+  doGenSelectParamsJson(const std::string& status,
+                        const std::list<std::string>& paramList) override;
+
+  JsonSection
+  doGenValidateParamsJson(const std::string& status,
+                          const std::list<std::string>& paramList) override;
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  void
+  parseConfigFile();
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  static const std::string FAILURE_INVALID_CREDENTIAL;
+  static const std::string FAILURE_INVALID_FORMAT;
+  static const std::string JSON_CREDENTIAL;
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  std::list<security::v2::Certificate> m_trustAnchors;
+  std::string m_configFile;
+};
+
+} // namespace ndncert
+} // namespace ndn
+
+#endif // NDNCERT_CHALLENGE_CREDENTIAL_HPP